Electromagentic flowmeter apparatus

ABSTRACT

Electromagnetic flowmeters wherein voltages induced in a conductive fluid flowing through magnetic fields having boundaries defined by magnetic cores impress voltages on the cores which are in turn coupled to output circuitry by electrodes connected to the cores.

United States Patent [151 3,696,674 Spencer [451 Oct. 10, 1972 [54]ELECTROMAGENTIC FLOWMETER 3,184,966 5/1965 Thornton et a1 ..73/194 EMAPPARATUS 3,372,589 3/ 1968 Mannherz ..73/194 EM [72] Inventor: MerrillP. Spencer 5151 K e nilwo 11h 3,487,826 1/1970 Barefoot ..128/205 FPlace NE. Seattle wash. 98105 ,516,399 6/1970 Barefoot ..128/205 F3,529,591 9/1970 Schuette ..73/l94 EM X [22] Filed: June 19, 1968 vPrimary Examiner-Charles A. Ruehl [21] Appl. No..- 738,306Attorney-Seed, Berry & Dowrey [52] US. Cl ..73ll94 EM, 128/205 F [57]ABSTRACT [51] Int. Cl. ..G0lp 5/08 Electromagnetic flowmeters whereinvoltages induced [58] Field of Search ..73/l94 EM, 128/205 F in aconductive fluid flowing through magnetic fields [56] References Citedhaving boundaries defined by magnetic cores impress voltages on thecores which are in turn coupled to output circuitry by electrodesconnected to the cores.

19 Claims, 8 Drawing Figures PATENTEDncI 10 I972 SHEEI 1 0F 2 M ERRILLP. SPENCER INVENTOR.

ATTORNEYS PATENTED 10 I 3 696, 674

sum 2 0F 2 MERRILL P. SPENCER INVENTOR.

AT TOR NE YS ELECTROMAGENTIC FLOWMETER APPARATUS BACKGROUND OF THEINVENTION The present invention relates generally to fluid flowmetersand specifically it relates to the magnetic core and electrode structureof electromagnetic flowmeters.

Electric flowmeters are in principal similar to dynamo generators. In agenerator, a conductor (a winding of a coil) traverses a uniformmagnetic field so as to cut magnetic lines of force at right angles. Ane.m.f. or voltage is induced in the conductor which is picked up throughbrushes connected to the ends of the conductor. In a flowmeter, thegenerator rotor is replaced by a conduit carrying a conductive fluid.The fluid flows so as to cut magnetic lines of force at right anglestherebytinducing an e.m.f. in the fluid. The induced voltage is pickedup through the walls of the conduit which serve a function similar tothat of brushes in the generator. The induced voltage is proportional tothe velocity of fluid and provides an instantaneous report on thevelocity of the fluid which can be displayed or recorded at a monitoringstation.

Lines of equal voltage potential induced in the fluid correspond to thedirectional lines, i.e., flux lines, of the magnetic field. Therefore,placing electrodes across the field on a line orthognal to the fluxlinesis a method for reading out voltages induced in the fluid. However,if the field varies in time, I such as that produced between the polesof an alternating current (AC) magnetic coil, a transformer effectinduces voltages on the electrodes in addition to those sought to, bemeasured. The location of the electrodes tends to maximize thetransformer effect because they are positioned directly in the magneticfield. Direct current (DC) magnetic coils are not common inelectromagnetic flowmeters because of electrolytic effects occuring atthe electrodes.

The present invention eliminates the requirement for inserting read outelectrodes or leads into the magnetic field. The leads are insteadconnected directly to the core of a magnetic c'oil so that the core alsoserves as electrodes. Surfaces of the core are placed in contact withthe flowing fluid. A voltage related to the flow .induced voltage andtherefore to fluid velocity is impressed on the core. The core voltageis communicated to output circuitry by a lead coupled to the core at aposition outside the field through which the fluid flows. This reducesthe transformer effect. Greater accuracy is possible if two paired coresare used to establish symmetrical magnetic fields. Voltages on the coreshave substantially the same magnitude, assuming equal fluid flow througheach field, and by proper handling of polarities the voltages can besummed. The sum of the two voltages may offer a more reliable indicationof the fluid velocity.

The present invention is especially advantageous in medicine where thesimplified structure allows for miniaturization and the reducedtransformer effect improves the detection of small flo'w inducedvoltages.

Miniaturizationis important, in catheter flow meters whichareinstruments designed to be inserted into the. lumen of a blood vessel. Aflowmeter. incorporated in a Another advantage of the present inventionis that surfaces of the core are at the locations of greatest fluxdensity and therefore at locations where the flow induced voltages areat a maximum.

It is accordingly the object of the present invention to devise animproved electromagnetic flowmeter and further to simplify the structureof a flowmeter by detecting impressed core voltages using electrodesattached to the cores and in particular it is an object of the presentinvention to devise improved structures for catheter and heart valveflowmeters.

DESCRIPTION OF THE DRAWINGS Other objects and features of the presentinvention will be apparent from a reading of the present specificationand from the drawings which are:

FIG. 1 is a perspective view of an electromagnetic catheter flowmeterand associated energizing and read out circuitry represented in blockform;

FIG. 2 is an enlarged perspective view of the catheter flowmeter in FIG.1 reversed illustrating the internally located magnetic coil, cores andelectrodes of the flowmeter; v

FIG. 3 is a cross-section elevation view of the flowmeter of FIG. 2including an illustration of the direction of the magnetic fields andthe relative polarity of voltages induced in a fluid flowing into thepage;

FIG. 4 is a perspective view of another embodiment of an electromagneticcatheter flowmeter employing two magnetic coils orientated with theiraxes parallel to that of the primary axis of the catheter;

FIG. 5 is a perspective view of a heart valve having an electromagneticflowmeter according to the present invention incorporated therein;

FIG. 6 is an end view of the heart valve shown in FIG. 5 as seen whenviewed from the right side;

FIG. 7 is a cross-section view of the heart valve in FIG. 6 as viewedalong lines 7-7 therein; and

FIG. 8 is a top view of another embodiment of a flowmeter structuresimilar to that of the heart valve incorporated in a clothes pin typestructure suited for clamping onto a fluid conduit. 7

A flowmeter generally connotates an instrument for measuring a unitvolume of fluid flow per unit time. In the present specificationflowmeter is intended to include velometry, i.e., the measurement oflocal velocities in a fluid stream. of course, given the velocityprofile of a fluid stream and the dimensions of its conduit, volume flowper unit of time of the fluid can be determined. Empirical calculationsof average velocity and of volume flow per unit can be made from localvelocity information. 7

FIG. 3 shows the general'direction of flux lines in the fields aboutcatheter l and the relative polarity of voltages induced in a fluidassumed to be flowing into the page along the primary axis of thecatheter. The direction of the voltage is orthogonal to the flux lines.

The catheter comprises magnetic coil 2 wound about between the endsurfaces of cores 3 and 4. The

direction of the magnetic field flux lines is given generally by arrows9. The direction of the arrows changes by 180 degrees on a time basisaccording to the change in the alternating current (AC) circuit drivingmagnetic coil 2. Direct current (DC) circuits may be used as well as apermanent magnet but the AC magnet means is presently preferred.

Catheter 1 is designed for insertion along its primary axis la into thelumen of a blood vessel, i.e., directly into the passage of a conduit.Blood, a conductive fluid, flows through the fields in gaps 7 and 8. Theflux density of the field through which the fluid flows is the greatestnear the core surfaces in contact with the fluid. Voltages are inducedin the fluid in areas occupied by the fields. The core end surfacesgenerally defining boundaries of the field through which a fluid flowsare orientated relative to the field such that the flux lines are noteverywhere normal to these surfaces. Therefore, the flow inducedvoltages adjacent the end surfaces of the cores are impressed on thecores. The voltages on the cores result from the flow of blood relativeto the catheter through the fields and are related to the velocity ofthe blood at the points where the cores contact the blood. The corevoltages are transmitted to the output circuitry by the electrode leadsl4 and 15, physically connected to the cores. Two cores are used becauseof the small magnitude of the voltages sought to be measured. The sum ofthe two flow induced voltages is easier to detect and if averaged mayprovide a more accurate indication of fluid velocity. The polarity ofthe core signals can be reversed relative to each other to assist in asumming or averaging process by either electrical techniques in theoutput circuitry or by reversing the direction of the flux lines in thefields relative to each other. The detected voltages, without attemptingto assign quantitative values to their magnitudes, may be used toobserve direction of fluid flow and its rate of change. Calibration ofthe voltages permits information to be obtained in regard to specificvelocity values and from this information volume flow per unit time canbe determined.

The output circuitry 6 supplies the electrical energy to coil leads 3aand 4a for driving the magnetic coil and provides the display means forreading out the voltages between electrode leads l4 and electricallyconnected to the cores. The preferred embodiment of circuitry 6 includesa square wave electromagnetic flowmeter circuit described in an articlein The Review of Scientific Instruments, V0. 27, No. 9, pages 707-7l I,September, I965, by A. B. Denison, Jr. and M. P. Spencer, the presentinventor.

The square wave circuitry employs, after its name, a square waveexcitation signal to drive magnetic coil 2. Use of the square wavesignal offers the flowmeter many of the advantages of both AC and DCcircuits. The square wave generator establishes the alternating fieldrequired to avoid electrolysis while at the same time providing atemporary steady-state signal. A blanking circuit separates thetransformer portion of the output signal from the measured voltage.

A flowmeter having the structure generally of that shown in FIGS. 2 and3 has been made using No. 38 iron wire as cores 3 and 4. The windings ofthe magnetic coil 2 are made from No. 44 copper wire. The coils andcores are embedded in a clear plastic insulating material 5 toelectrically isolate the windings of the coils from each other and fromthe cores. The cores are insulated from each other and from the coils.The insulating material also forms the case of the catheter. Surfaces 17and 18 on both cores 3 and 4 extend through the plastic insulatingmaterial 5 and are flush with the plane surface 11 on the generallycircular cross-section of the catheter. They contact fluid flowing pastthe catheter. The surfaces 17 and 18 may be coated with a non-corrosiveor electrolytically inert conductive material. The core may comprise ofstainless steel rather than iron or any other material of satisfactorypermitivity chemically compatible with the fluid with which it is to beused.

The flowmeter in FIG. 4 is another embodiment of a catheter instrument.It has two magnetic coils. Cores 20 and 21 are shaped to form rightangles at points 24. They also have surfaces 17 and 18 for contacting afluid. This permits the magnetic coils 22 and 23, or a single coil, tobe wound around the cores as shown with their axes extending along theprimary axis of the catheter. A single coil can be used in place of thetwo coils if its windings surround both cores. This embodiment permitsthe two coils or a single to have a greater number of windings andtherefore to generate a larger amount of flux. Also, the arrangement ofthe cores enables the electrode leads 25 and 27 to be physicallyconnected to the cores at the places shown which is even further removedfrom the magnetic field thereby reducing the transformer effect. Otherarrangements of the cores can be devised to permit the electrode leadsto be connected to the cores in a similar manner and to permit a coil tobe wound with its axis parallel to the primary axis of the catheter. Anexample would be to shape the cores generally as those in FIGS. 2 and 3,rotate the cores and coil degrees relative to the catheter and laterallyoffset the exposed tips 17 and 18 to orientate the flux linesperpendicular to the primary axis of the catheter. The electrode leads25 and 27 are terminated in an output circuit of the square wave type asdescribed earlier. Likewise the terminals of the magnetic coils 22 and23 are coupled to a square wave generator in the output circuitry.

Heart valve 30, shown in FIG. 5, has incorporated about its periphery aflowmeter employing magnetic cores and electrodes according to thepresent invention. As best seen in FIG. 7, the cores 32 and 33 areinsulated from the heart valve ring 36 through which blood flows by asuitable electrical insulating material 31. The insulating material alsocovers magnetic coils 34 and 35 wound around the two cores. The endsurfaces of cores 32 and 33 extend through the inner periphery of thering 36 at four points 39. Points 29 are surfaces of the cores whichcontact blood flowing through the valve and are flush with the innerwalls of ring 36. FIG. 6 illustrates the magnetic fields through whichblood flows. The fluid flowing through the magnetic fields has voltagesinduced in it. The induced voltages near the core surfaces at points 39are impressed on the cores. The voltages on the two cores are sensed ordetected by electrode leads 37 and 38, physically connected to cores 32and 33. These leads are terminated in appropriate output circuitry asdescribed earlier. Coil leads 34a and 35a are preferably coupled to anappropriate square wave generator as described earlier. Apron 31a is adevice for enablingthe heart valve to be sewed or otherwise secured to ahuman or animal heart.

The clothes pin type structure shown in FIG. 8 is a flowmeter accordingto the present invention. This device is designed primarily for clampingonto the walls of a blood vessel. The walls of the conduit mustbe atleast partially conductive to enable the cores to electrically contact afluid flowing therein. The structure of cores 40 and 42 and coils 49 and50, and the operation of the device is similarto that of the heartvalve.

The clothes pin type structure enables the flowmeter 41 at one end ofthe clothes pin to be expanded for clamping it onto a conduit. Theflowmeter 41 is shown clamped onto conduit 46. Legs 43 and 45 arebrought together at the end opposite the flowmeter 41 to expand thedevice. The spring 44 maintains or urges the ends containing flowmeter41 together and the opposite ends apart.

Surfaces of the cores, at points 48, contact the walls of' conduit 46.Voltages induced in the fluid are im-.

pressed on the'cores at points 48 through the wallsof the core surfaceat points 48. The output electrode leads 52 and 53 are physicallycoupled to the cores 40 and 42 and are coupled to appropriate outputcircuitry where the voltages impressed on the cores are either recordedor displayed. a

It is believed that the invention will have been clearly understood fromthe foregoing detailed description of my now-preferred illustratedembodiments. Changes in the details of construction may be resorted towithout departing from the spirit of the invention. it is apparent thatthe catheter flowmeter may be adapted for measuring the velocity offluids other than blood. Also, the embodiments incorporated in the heartvalve and clothes pin type structures may be readily adapted to otherconfigurations. Specifically, the core and electrode arrangement of theforegoing devices may be permanently installed about a cross-section 'ofany fluid carrying conduit to provide permanent fluid flow monitoring.In addition, it should be understood that the various core and electrodestructure of the present invention may be employed in apparatus formeasuring the velocity of a vehicle through a stationary fluid. In thisregard, the present invention pertains to relative velocities between afluid and a core regardless which of the two moves relative to a commonreference frame. Accordingly, it is my intention that no limitations beimplied and that the hereto annexed claims be given the broadestinterpretation to which the employed language fairly admits.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An electromagnetic device for sensing voltages induced in aconductive fluid material moving relatively through a magnetic fieldcomprising cal circuit is completed through the fluid material.

2. The device of claim 1 wherein said magnet means includes a permanentmagnet.

3. The device of claim 1 including at least two of said magnet means forestablishing at least two magnetic fields, each of said magnet meansbeing electrically connected to said sensing means.

4. The device of claim 3 wherein said two magnetic fields aresubstantially symmetrical and substantially the same size and patternand wherein the ferromagnetic electrically conductive section of each ofsaid magnet means has a shape to form said fields in said manner. g

5. The device of claim 1 wherein said magnet means comprises v at leastone magnetic coil for producing magnetic flux when coupled to a sourceof electrical energy, the ferromagnetic electrically conductive sectioncomprising at least two magnetic cores positioned in the path of saidflux for forming plural magnetic fields through which the fluid flows,said cores contacting the fluid flowing through said fields, and

means for coupling said coil to a source of electrical energy.

6. The device of claim 5 further including insulating material forelectrically insulating said cores from each other and from saidmagnetic coil.

7. The device of claim 5 wherein said magnet means further includes analternating current electrical energy source connected to said couplingmeans.

8. The device of claim 5 wherein said sensing means includes electricalleads electrically connected to said cores.

9. The device of claim 8 wherein said sensing means further includeincludes square-wave flowmeter circuitry.

10. The device of claim 1 wherein said ferromagnetic electricallyconductive section comprises a magnetic core disposed for electricalcontact with said fluid material at surfaces near the ends of said core,and wherein said magnet means comprises a magnetic coil wound about saidcore, and wherein said sensing means includes an electrical leadconnected to said core.

11. The device of claim 10 in combination with a clothes pin typestructure for clamping onto the walls of an electrically conductiveconduit including two legs and a'spring operatively coupled together,one end of said legs expanding when the legs are brought together atanother end; wherein two of said magnet means are contained, one in eachleg with a core, coil and electricallead operatively mounted on each ofsaid legs at the expandable end thereof, with surfaces of said corespositioned to contact the conduit when placed between the expandableends.

12. The combination of claim 11 wherein said sensing means comprisesoutput means coupled to said electrical leads to display voltagesimpressed on said cores in response to voltages induced in a fluidflowing through the conduit and further including an alternating currentsource of electrical energy coupled to said magnetic coils.

13. A catheter flowmeter for insertion along a primary axis of theflowmeter case into the lumen of a fluid conduit comprising;

at least one magnetic coil for generating magnetic flux when said coilis coupled to a source of electrical energy,

at least two magnetic electrically conductive cores inserted in the pathof said flux directing said flux to form at least two magnetic fieldsperpendicular to said primary axis through which the fluid flows, eachcore having an exposed electrically conductive surface for electricalcontact with fluid material flowing through the fluid conduit orientedwith respect to its respective magnetic field so that flow inducedvoltages will be impressed on said surface, and

an electrical lead connected to each of said magnetic cores.

14. The device of claim 13 further including means coupled to saidelectrical leads for monitoring voltages impressed on said cores inresponse to a voltage induced in a fluid flowing through said magneticfields.

15. The flowmeter of claim 13 wherein said magnetic coil is orientedwith its axis perpendicular to said primary axis, and

said two magnetic cores have ends which define boundaries of saidmagnetic fields through which the fluid flows and are inserted withinthe windings of said coil, said ends each providing a said electricallyconductive surface substantially flush with the surface of saidflowmeter case contacting the flowing fluid,

said cores positioned relative to each other to form said magneticfields substantially apart relative to the flowmeter case and insubstantially the same plane 16. The flowmeter of claim 15 furtherincluding an alternating current energy source coupled to said magneticcoil.

17. The flowmeter of claim 15 wherein said flowmeter case has asubstantially circular cross-sectional shape except in the areas of saidcore ends where said case has substantially a plane shape. 7

18. The flowmeter of claim 17 wherein said case comprises an electricalinsulating material for insulating said cores from each other and saidmagnetic coil.

19. The flowmeter of claim 13 wherein said magnetic coil is orientedwith its axis parallel to the primary axis of the flowmeter, and wheresaid two magnetic cores have ends defining boundaries of said magneticfields through which a fluid flows and are positioned within thewindings of said coil oriented relative to each other to locate saidmagnetic fields relative to the case of the flowmeter in substantiallythe same plane.

1. An electromagnetic device for sensing voltages induced in aconductive fluid material moving relatively through a magnetic fieldcomprising magnet means to produce the magnetic field, said magnet meanshaving a ferromagnetic electrically conductive section through whichextend flux lines of the magnetic field, said section having anelectrically conductive exposed surface for electrical contact with thefluid material moving relatively through the magnetic field orientedwith respect to the magnetic field so that flow induced voltages will beimpressed on said surface, and sensing means electrically connected tothe said section of said magnet means for detecting flow inducedvoltages impressed thereon when an electrical circuit is completedthrough the fluid material.
 2. The device of claim 1 wherein said magnetmeans includes a permanent magnet.
 3. The device of claim 1 including atleast two of said magnet means for establishing at least two magneticfields, each of said magnet means being electrically connected to saidsensing means.
 4. The device of claim 3 wherein said two magnetic fieldsare substantially symmetrical and substantially the same size andpattern and wherein the ferromagnetic electrically conductive section ofeach of said magnet means has a shape to form said fields in saidmanner.
 5. The device of claim 1 wherein said magnet means comprises atleast one magnetic coil for producing magnetic flux when coupled to asource of electrical energy, the ferromagnetic electrically conductivesection comprising at least two magnetic cores positioned in the path ofsaid flux for forming plural magnetic fields through which the fluidflows, said cores contacting the fluid flowing through said fields, andmeans for coupling said coil to a source of electrical energy.
 6. Thedevice of claim 5 further including insulating material for electricallyinsulating said cores from each other and from said magnetic coil. 7.The device of claim 5 wherein said magnet means further includes analternating current electrical energy source connected to said couplingmeans.
 8. The device of claim 5 wherein said sensing means includeselectrical leads electrically connected to said cores.
 9. The device ofclaim 8 wherein said sensing means further include includes square-waveflowmeter circuitry.
 10. The device of claim 1 wherein saidferromagnetic electricallY conductive section comprises a magnetic coredisposed for electrical contact with said fluid material at surfacesnear the ends of said core, and wherein said magnet means comprises amagnetic coil wound about said core, and wherein said sensing meansincludes an electrical lead connected to said core.
 11. The device ofclaim 10 in combination with a clothes pin type structure for clampingonto the walls of an electrically conductive conduit including two legsand a spring operatively coupled together, one end of said legsexpanding when the legs are brought together at another end; wherein twoof said magnet means are contained, one in each leg with a core, coiland electrical lead operatively mounted on each of said legs at theexpandable end thereof, with surfaces of said cores positioned tocontact the conduit when placed between the expandable ends.
 12. Thecombination of claim 11 wherein said sensing means comprises outputmeans coupled to said electrical leads to display voltages impressed onsaid cores in response to voltages induced in a fluid flowing throughthe conduit and further including an alternating current source ofelectrical energy coupled to said magnetic coils.
 13. A catheterflowmeter for insertion along a primary axis of the flowmeter case intothe lumen of a fluid conduit comprising; at least one magnetic coil forgenerating magnetic flux when said coil is coupled to a source ofelectrical energy, at least two magnetic electrically conductive coresinserted in the path of said flux directing said flux to form at leasttwo magnetic fields perpendicular to said primary axis through which thefluid flows, each core having an exposed electrically conductive surfacefor electrical contact with fluid material flowing through the fluidconduit oriented with respect to its respective magnetic field so thatflow induced voltages will be impressed on said surface, and anelectrical lead connected to each of said magnetic cores.
 14. The deviceof claim 13 further including means coupled to said electrical leads formonitoring voltages impressed on said cores in response to a voltageinduced in a fluid flowing through said magnetic fields.
 15. Theflowmeter of claim 13 wherein said magnetic coil is oriented with itsaxis perpendicular to said primary axis, and said two magnetic coreshave ends which define boundaries of said magnetic fields through whichthe fluid flows and are inserted within the windings of said coil, saidends each providing a said electrically conductive surface substantiallyflush with the surface of said flowmeter case contacting the flowingfluid, said cores positioned relative to each other to form saidmagnetic fields substantially 180* apart relative to the flowmeter caseand in substantially the same plane.
 16. The flowmeter of claim 15further including an alternating current energy source coupled to saidmagnetic coil.
 17. The flowmeter of claim 15 wherein said flowmeter casehas a substantially circular cross-sectional shape except in the areasof said core ends where said case has substantially a plane shape. 18.The flowmeter of claim 17 wherein said case comprises an electricalinsulating material for insulating said cores from each other and saidmagnetic coil.
 19. The flowmeter of claim 13 wherein said magnetic coilis oriented with its axis parallel to the primary axis of the flowmeter,and where said two magnetic cores have ends defining boundaries of saidmagnetic fields through which a fluid flows and are positioned withinthe windings of said coil oriented relative to each other to locate saidmagnetic fields relative to the case of the flowmeter in substantiallythe same plane.